``test_functools`` sometimes leaks references

The text below is a part of the refleak tests, and unfortunately, I am unable to constantly reproduce it :(

0:13:26 load avg: 7.84 [201/478/1] test_functools failed (reference leak) -- running (3): test.test_multiprocessing_spawn.test_processes (7 min 14 sec), test_embed (1 min 12 sec), test_faulthandler (55.3 sec)
beginning 6 repetitions. Showing number of leaks (. for 0 or less, X for 10 or more)
123:456
XX1 111

從 CPython 針對 test_functools 的 refleak 測試輸出開始，並嘗試在 refleak runner 下反覆執行該測試。該報告是間歇性的，且未提供原始碼檔案或 reproducer，因此首先要隔離出哪個測試路徑會洩漏參照。完成標準是找出發生洩漏的路徑，並新增一個能防止該洩漏的 regression fix 或測試。